Assuming you have the Scepter, you can just run in the closest instance entrance - that will rezz you. Then you leave the instance and go to the portal chamber and use your scepter...

The best way to tell what level an instance should be played is by looking at the loot of the bosses.

Very hard fights are those where you may get blue items your level.

Since the drops in Maraudon are level 46-49 thats about the level your group needs. If you want to do the whole instance you should have a group of chars at level 48 at least so you have all the newest spells.

I got into Mara at 38 - Had a 55 druid holding aggro (feral spec I think), a frost mage (lvl 57), a warlock (lvl 51) and a hunter (lvl 41) in my group. We went to Inner Maraudon and we managed to defeat the 8 or so Rock Elementals around lvl 49 elite.

It was an intense battle, both the druid and the hunter died, but the rest of the party including me survived. It was an intense job as healer trying to keep the group alive. I have 3k mana and I was constantly running out, but I managed to keep 3 out of 5 alive, in that intense fight. I had only just healed our warlock just in time so that he didn't die, and my mana was extremely low. I had to resort to using all my very useful discipline-based spells such as Inner Focus and I did use Desperate Prayer to keep myself alive (I'm a dwarf priest). Frost Nova came in very handy from the mage. She managed to keep me alive and get the aggro off of me, as as she and the lock started casting their spells on that particular rock elemental.

Our entire group was surprised even I managed to survive along with the other 2. Being out of mana, and being able to keep 3/5 people in the group alive with an odd 8 or 9 or so rock elementals fighting us was quite a feat. We did not go on to anything much further than that apart from the giants. Our group didn't believe we could do Princess or anything much harder than those rock elementals. We had a big job trying to stay alive, and so my advice is, if you're around lvl 39/40, get some mid to high 50's to combat Mara (even a 60 if you can) and I believe it would certainly be possible.

Sorry about the long post but I hope it has given some insight into those wanting to do Mara early (I wanted most of the cloth drops, so that I could improve my char and work towards getting my mount quickly). There is still a fair amount of aggro around those lvls - until you hit around 48 or so, you would need a high lvl tank to help you in Mara. I hope this helps!

mara is level 48+ and STILL people are picky about inviting you.... 50+ if you're tanking but a caster or healer is good at 48

Valley of Spears it's called, occupied by centaurs on west side of Desolace, near the south by the horde village. If you look on the map in Valley of Spears, it's the cave marked on the map.